The Frost Dungeon
They descended for a long while. The stair spiraled down with no terminus in sight. The light seemed to lead them. The walls grew damp, cold, colder, coming to be covered with a fine patina of frost figures.
Roger Zelazny – Dilvish, the Damned
I like the idea of sensory details, like temperature, informing a dungeon, and there are a lot of dungeon tricks that can be done with ice, especially if one of the PC is a fireball-toting wizard. Furthermore, if the PCs are defeated in an ice dungeon, they’re sure to wake up hanging upside down from the ceiling just as a Wampa beast shows up for dinner.
The Star Labyrinth
“As for myself, in my early years I beamed through the star-labyrinth many times. Why, once I accompanied Priestess Poogli all the way to–”
Emil Petaja – The Nets of Space
Just as the ocean is a dungeon, space can be a dungeon. Let’s say that each star leads only to 2-3 other stars (because of stargates, distance, spice, or some other such nonsense). The PC’s space ship, spelljammer, or astral kayak is essentially plying a space dungeon, with planetary systems as rooms and navigation routes as corridors.
“The Star Labyrinth” is also a cool name. As cool as Princess Poogli? Hard to say.
The Drowned City
Riding along the fringes of this wild place, Orisian could see, faint in its misty heart, the ruined towers of old Kan Avor. The broken turrets and spires of the drowned city rose above the waters like a ghostly ship on the sea’s horizon.
-Brian Ruckley – Godless World: Winterbirth
A half-submerged city is not a completely unique adventure locale: many platformer video games have a water dungeon where you have to pull levers to change the water level. It’s still a cool spot, and if the PCs have to do some dangerous diving to get to the entrance of a half-submerged tower, you can give them some interesting challenges on the way up the tower: a time limit based on holding your breath, for instance. Another fun aspect of amphibious adventuring is that swimming PCs can easily escape water-only enemies, like sharks, and air-only enemies, like birds. You can use this to introduce some difficult puzzle enemies: if the fight is impossible, the PCs can easily submerge, or emerge, to safety.